Polyethylene terephthalate (PET) and its copolyesters are widely used polymers for making packaging articles in part due to their excellent combination of clarity, mechanical, and gas barrier properties. The raw materials used in the manufacture of commercial PET polymers are purified terephthalic acid (PTA), or its dimethyl ester (DMT), and monoethylene glycol (MEG), all of which are derived from petroleum feedstocks. In many applications other comonomers are added to reduce the rate of crystallization of the PET resin during the manufacturing of the article. Typical crystallization retardants are isophthalic acid (IPA), cyclohexane dimethanol (CHDM), succinic acid (SA), and 2,5-furan dicarboxylic acid (FDCA). Branching agents, such as trimellitic based acids, are used in copolyesters where high melt strength is required for processing, for example extrusion blow molding. Currently all these comonomers are derived through petrochemical processes.
The polyester industry is actively developing processes for PTA and MEG which are based on renewable plant-based feedstocks. The advantages are reducing the carbon footprint of PET manufacturing, reducing greenhouse gas emissions and the use of a sustainable feedstock not tied to the price of oil.
Bioethanol can be produced from biomass by the hydrolysis and sugar fermentation processes. Biomass wastes contain a complex mixture of carbohydrate polymers from the plant cell walls known as cellulose, hemi-cellulose, and lignin. In order to produce sugars from the biomass, the biomass is pre-treated with acids or enzymes in order to reduce the size of the feedstock and to open up the plant structure. The cellulose and the hemi-cellulose portions are broken down (hydrolyzed) by enzymes or dilute acids into sugars that are then fermented into bioethanol. The bioethanol can be dehydrated to bioethylene from which bio monoethylene glycol—bioMEG can be produced by current chemical processes, without the use of any non-biomass chemicals, i.e. without petroleum based materials. Manufacturing facilities in India and Brazil are currently manufacturing and selling bioMEG.
Coca-Cola purchases polyester resin made from bioMEG and PTA for bottles sold under their PlantBottle® trademark. The biobased content of these bottles is about 32% from the bioMEG. There is active research and development to commercialize bioPTA such that all the major monomers (PTA and MEG) are made from biomass feedstocks. Several companies have pilot plants that convert biomass into p-xylene, which is then oxidized into bioPTA by the current PTA manufacturing process.
U.S. Patent Application 2009/0246430 discloses a method to manufacture bioPET. This bioPET comprises 25 to 75 wt. % of terephthalate compound selected from terephthalic acid, dimethyl terephthalate, isophthalic acid, and a combination thereof. It also comprises 20 to 50 wt. % of diol compound selected from ethylene glycol, cyclohexane dimethanol, and a combination thereof. At least 1 wt. % of the terephthalate compound and/or the diol compound is obtained from biomaterials. The bioPET of U.S. 2009/0246430 can be used for manufacturing beverage containers. However this application does not disclose the use of comonomers derived from biomass in their composition such comonomer as bioisophthalic acid (bioIPA) or biotrimellitic anhydride.
U.S. Patent Application 2011/0288263 discloses benzene 1,4-dicarboxylate compounds (terephthalic acid and carboxylate derivatives thereof, such as trimellitic based acids), and cyclohexane 1-4-dicarboxylate derivatives based from renewable resources. The use of muconic acid in the processes described to make these dicarboxylate derivatives, can be made from biomass, for instance by the process described in U.S. Pat. No. 5,616,496. The polyesters prepared from these monomers based on muconic acid from biomass will therefore be partially based on biobased raw materials.
U.S. Patent Application 2014/0197580 discloses a method for producing a bioPET using up to 7.5 mol % of a crystallization retarding compound. However the crystallization retardant comonomers disclosed are not produced from biomass.
It is clear that the industry will be moving to the use of bioMEG and bioPTA to manufacture bioPET. However in many applications, for example injection stretch blow molded bottles for carbonated soft drinks and water, crystallization retardants are added as comonomers in a range of about 2 to 5 mole %, based on the total copolyester, to minimize any haze in the container that would reduce clarity. Similarly comonomers such as isophthalic acid, neopentyl glycol, cyclohexanedimethanol and others are used at higher levels for amorphous copolyesters for use in sheets for thermoformed articles, shrink-films and the like. Branching agents, monomers with more than 2 functionalities, are also used for certain applications such as extrusion blow molded containers.
There is therefore a need for comonomers derived from biomass to substitute for these comonomers currently produced from petroleum feedstocks.